The best way is to avoid the mac altogether. I use a mac as my main computer, but I use my old Dell laptop whenever I upgrade--also because I use shrinkOS. You may not have a PC but you must know someone who does...

Also, the few times I tried to use my mac, I got a startup error on my Storm. Not so using a PC. To answer your questions: it is possible, but you can't really control it. Mac DM checks for official releases/updates automatically (from what I understand).